Telephone system



Sept. 12, 1944.

B. F. I Ewls ETAI.

TELEPHONE SYSTEM Filed Dec. 22, 1942 12 Sheets-Sheet l /NL/EwmffsfsQS'ept. 1,2, 1944. B. F. I Ewls ET Al.

TELEPHONE SYSTEM l2 Sheets-Sheet 2 Filed Dec. 22, 1942 III, ||I|I IIIIIl. III llllllll .lIl

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TELEPHONE SYSTEM Filed Dec; 22, 1942 12 Sheets-Sheet 3 F. Ew/s MUM/VERI/VVENTORS! W A Arkon/vw sept. 12, 1944.

B. F. Ll-:wls ET AL 2,358,237

TELEPHONE SYSTEM I Filed Dc. 22, 1942 12 SheefS-Sheet 4 A .stfLEW/s/NVENTO/ n/.AMALTHANER ATTORNEY Sept. 1 2, 1944. B. F. L Ewls ET Al. t.2,358,237

` TLEPHONE SYSTEM :Filed Dec. 22, 1942 12SheeLS-Sheet- 5 /NVEA/ro/es:

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B W. MALTHANE/P ATTORNEY Sept. 12, 1944.4

B. F. LEw|`s ETAL 2,358,237

TELEPHONE SYSTEM l Filed Dec. 22, 1942 12 sheets-sheet e Afro/MEV Sept.12, 1944. B. F. LEWIS ET AL TELEPHONE -SYSTEM Filed Dec. 22, 1942 l2Sheets-Sheet 7 ELEW/s www 14./ AUHANER ATTORNEY Sept. 12, 1944. B. F.LEWIS ET AL 2,358,237

A TELEPHONE SYSTEM Filed Deo. 22, 1942 12 Sheetsfsheet 8 L/NK CONNECTOR/2.

MAL'HANER BV l Sept. l2, 1944. B. F. LEwls ETA. 2,358,237

TELEPHONE SYSTEM Filed Dec. 22. 1942 12 sheets-sheet 9 TRANS/.A TOR CC7:

y /NvE/vrO-Rs: BfLEW/S WA. THANER BV i ArToR/Ey Sept. 12,' 1944. B. F.LEwls ETAL TELEPHONE SYSTEM v12 Sheets-sheet 11 Filed D66. 22, 1942 ATTURA/EV sept. 12, 1944. a. F.' pms., TAL

Y 2,358,237 TELEPHONE sYs'rEM A ,y

12 sheets-sheath Filed Dec. 22. .1942.

/M/Nr'ons arf-.LEWIS ATTORNEY Patented Sept. 12, 1944 TELEPHONE SYSTEMBenjamin F. Lewis, Bayside, and William A. Malthaner, New York, N. Y.,assignors to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 22, 1942,Serial No. 469,778 .5 claims. (ol. 17a- 27) This invention relates totelephone systems and particularly to small capacity telephone systemsof the private branch exchange type (P. B. X) in which cross barswitches are employed. More particularly, the invention is in the natureof an improvement over the small capacity telephone system disclosed inuPatent 2,300,951, issued to W. A. Malthaner on November 3, 1941, inwhich means are provided whereby the telephone lines or stationsequipped with Ydifferent types of call sending devices may operatecommon apparatus by which to set up desired connections such as, forinstance, between a station that utilizes a dial sender to transmit aseries of impulses designating a called number and a station thatutilizes an alternating current generating device to operate and-transmit combinations of different frequencies to designate the callednumber.

In some P. B. X exchanges of the above type in which the P. B. Xsubscribers are also provided with facilities for establishing directconnections to the main central ofce over trunks interconnecting theoflice and the switching element of the P. B. X, the lines privileged toestablish trunk connections are provided with a key for each trunk whichmust be operated to connect the associated trunk with the line upon theinitiation of a call. When the branch exchange contains both privilegedand non-privileged lines, the non-privileged lines being restricted tolocal branch service only, circuit complications arise to distinguishand keep separate the two classes of lines.

According to the present invention the privileged lines are not providedwith trunk keys, and a feature of 'the invention is the provision of anarrangement whereby all outgoing and incoming trunk calls clear throughwhat may be called a control station at which the trunk keys and othernecessary equipment are concentrated, all lines desiring trunkconnections being required to dial or key the control station andrequestl the desired connection of the attendant thereat. The controlstation attendant then asks the calling party to restore, dials theoutside number over an available trunk and, when the wanted outsideparty answers, dials the number of the station originating the request.The trunk is then automatically extended back to this party without anyfurther assistance on the part of the control` station operator. A trunklamp associated with the engaged trunk apprises the control stationoperator that the call is established and the controlY operatorthereupon restores his receiver to eiect a breakdown of the localconnection between the control station and party originating the call.The trunkV is thereafter under the direct control of the originatingparty and when he restores, the trunk is restored to normal, propersignal facilities being provided to apprise the control station'operatorthat the trunk is then again available for service.'

A more specific feature of the invention is, therefore, a circuitarrangement in a P. B. X of the class described in which, on j anoutgoing trunk connection between the control station and the trunk andthe subsequent dia-ling of the calling line' by the control operator,the trunk is automatically caused to be extended 'back to said line toestablish thereby a talking connection thereover.

The invention is illustrated in connection with the following drawingsin which:

Fig. 1 shows two of the twenty stations in the P. B. X, station A havinga line designation of 39 and provided with an alterating current or keypulsing generating device LG, land station B having a line designation20 and provided with a dialing device LD. In the present embodiment ofthe invention, station B isutilized as the controlstation throughV whichall outside connections to and from any other station in the P. B.'X maybe established, said control station being always provided with adialing device LD,

while thev other nineteen stations inthe P. B. X-

may be provided with either a dialing device LD or a key pulsing deviceLG;

Figs. 2 and 3 show diagrammati'cally a cross bar switch frame vof knownconstruction having ten horizontal outlets and twenty verticals to eachof which vertical is connected a subscribers line.' The rst vertical isdesignated as vertical 20 and is assigned to control station line 2li(station Bi), the last vertical is designated as vertical 39 and isassigned to line 39 (station A), while theV intermediate verticals 2| to38 are each respectively assigned to a similarly designated line;

Fig. 4 in the left portion thereof, shows a link allotter circuit, whilethe rest of this gure and Fig. 5 show the call allotter circuit;

Figs. 6, '7, 8, 9 and l0 show the details of the link circuit;

Fig. 11 shows, in diagrammatic form, two other links and a powergenerating, tone and alarm circuit; v

Fig. 12. shows one two-way trunk in detail, said trunk interconnectingthe P. B. X with the central oflice, and three other trunks, conven- A;secondly, in respect to the operations neces-, sary to set up an outsidecall to the central olce' from station A, and, thirdly, in respect tothe operations necessary to establish an incomingr connection from thecentral olice` tostation A.

Before describing the detailed operation of the invention, however, itis desirable to call attention to the fact that the illustrativeembodiment of the invention is being shown in connection with a smalloflice having a maximum capacity of twenty'lines, each station of which,with the exception of the control station B, is equipped either with'adialjLD or a'generator'LG for transmitting VvCH3, which form a linkallotter circuit. Relays CHI and CH2 are shown in an operated positionwhile relay CH3 is shown in an unoperated posicalled line designations,said control station B being always provided with a dial Each lineappearsY on one of the twenty verticals of the cross bar switch,conventionally shown in Figs. 2 Vand 3,-and each line; for simplicity,has been given a numerical designation corresponding to the verticaltorwhich it is assigned.

The-dial LD visY the ordinary impulse dial well known ,in automatictelephony, and its manipulation `interrupts 'the'line to produce aseries of pulses the number of which, in Ya series, correspends Vtothedigit from nwhich the dial is pulled over to the stop attachment priorto releasing it for its return to normal, inthe course of which thetrain or series of impulses is produced. The deviceV LG, on thel otherhand, is an alternating current generator which, for example, may be of,the type-shown'in Patent No. 2,147,710 granted to R. F. Mallina onFebruary 21, 1939. It comprises 'a number of reeds which may be pluckedin pairs toproduce vibrations within a magnetic field and thereby causethe production of currents having frequencies determined by theirrespective physi- 'cal periodicities. A These currents are transmittedover the" link into registers therein for use in causinguthe link tocomplete the connection to the-desired line. Y

A For' the quantity of internal trafc which may arise ywithin the twentylines of the system, only three links are provided each occupying two'horizontal outletsof thecross bar switch,`link I (the circuit structureof which lis Yshown in detail in Figs 6 to 10, inclusive) occupying theVtwo uppermost outletscontrolled, for selective purposes, byselect-magnets 8 andS; link 2 occupying the two horizontal outletsimmediately below those of link -I and controlled by select magnets 6and 1, while link `3 occupies the two horizontal outlets immediatelybelow those of link 2 and controlled by select magnets 4 and 5. Theremaining four outlets of the switch are reserved for four interolnetrunks, trunk I (Fig. 12) being wired to the third horizontal outletcontrollable for selective purposes by select magnet 3, whiletrunks 2, 3and 4 are each wired to horizontal outlets 2, I and 0, respectively. Itis to be observed that the horizontal outlets for the links extendstraight across the frame, thereby giving each verticalV access toeachlink. The horizontal outlets for the four trunks, on the other hand,are not continuous. The upper group of trunk conductors designatedUSl'and UH are connected only to the cross-point of vertical 20on thethird horizontal tion. These three relays control the sequentialallotment of an, available link to a calling line and 'the function ofthe relays CHI and CH2 in the condition shown is to route the startconductor I to the first available link in the oice. As stated before,in the present embodiment of the invention itis assumed that thequantity of traine from and between the various lines of the office,including the control station B, may be properly handled by the use ofonly three links so that the relays CHI, .CH2 and CH3 serve to route acalling line to one of the three links depending upon which one is freein the order of allotment. The operated condition of relay CHl indicatesthat the link to which it provides access is in an idle condition, thelocking circuit of said relay extending from battery through the windingthereof, contacts of key 'KYL conductor 2, No. 1 back contacts of relayB of link No. 1 (Fig. 5), conductor 3, No.3 front contacts of relay CHIto ground. The locking circuit of relay CH2 which controls access tolink No. 2 is traced over a path which extends from battery through itswinding, contacts of key KYZ, conductor 2' in the bracket line 4,through the No. 1 back contacts of relay B in link No. 2 A(saidilinkbeing diagrammatically indicated in Fig. 10), conductor 3 in the bracketline 4, No. 6 contacts of relay CH2 to ground.

On the other hand, the operating circuit of relay CH3 which providesaccess'to link No. 3, while traceable over the contacts. of itsassociated key KY3, conductor 2 within bracket `line 5, through the No.1 backcontacts of relay B in link No. 3 (said'link beingdiagrammatically shown in Fig. l0) and conductor 3 within bracket line5, terminates in the No. 3 normal contacts of relay CH3 and also in theNo. 3 open contacts of relay CHI.v

In other words, for a calling line to have accessibility to link No. 1,relays CHI and CH2 must be operatedJ and relay CH3 must be normal. Itwill be shownthat, as each link is allotted in rotation, the circuits ofrelays CHI, CH2 and CH3 are changed to provide for the advancement ofstart conductor I from one link to the next in the order Vindicated bythe numerical indication of each of the three links.

Bearing in mind that relays CHI, CH2 are operated and that relay CH3 isnormal, it may now be assumed that a call is originated at controlstation B (line 20). The telephone instrument is removed from its cradleat said station and key L is operated. A circuit is now completed forrelay L20 of said line which extends from battery over the upper normalcontacts of the hold magnet H020 associated with vertical 20, winding ofrelay L20, ring conductor R, over the station loop, tip conductor T, No.l normally made contacts of relay L20 to ground on the No. 1 contacts ofcut-01T relay C020. Relay L20 operates. Over its No. 1 front contacts,the'ground terminal of its circuit is switched from solid ground on theNo. 1 contacts of relay C020 to ground through the secondary windingof-'transformer LBT to the primary winding of which is connected asource of distinctive tonewhich, as Will be described shortly, istransmitted to the calling line in the event that no linkis availablefor completing the connection. Y

Over its No. 2 and No. 3 contacts, relay L29 causes a circuit to becompleted for relay LO20 of the call allotter circuit (there being onerelay LO- for eachV line) and relay ST of link No. l which, since relaysCHI andCHZ of the allotter are assumed to be operated and relay CH3 isassumed to be normal, is the preferred link in the order of selection.The circuit for the relays ST and L20 is traced as follows: Groundthrough the No. 1 contacts of relay El, winding of relay LO20, conductor6, No. 3 contacts of relay L20, the No. 3 set of contacts closed by thetelephone instrument cradle, serially through normal contacts of thetrunk keys TKI, TKZ, TK3 and TKII, contacts of key L, No. 2. contacts cirelay L20, start conductor I, No. 3 contacts of relay CH2, No. 1contacts of relay CHI, conductor 1, winding of relay ST to battery. Bothrelays LO20 and ST operate in this circuit. Relay LO20, upon operating,completes a circuit for relay N the path of which may be traced fromground on the No. 1 contacts of relay L029, conductor I0, No. 1 backcontacts of relay M, No, 4 contacts of relay MS, winding of relay N toground. Relay N operates and completes a circuit for relay M whichextends from ground on the No. 2 contacts of relay N, No. l backcontacts of relay MS, winding 01|?l relay M to vbattery. Relay Moperates, opens the circuit of relay N at its No. l back contacts andcauses the latter relay to release. The release of relay N opens thecircuit of relay M but this relay, however, remains locked to ground onconductor I0 under the control of the No. `1 contacts of relay MS andits own No. 2 contacts. When relay MS operates as described below, relayM releases. This cycle for operating relays M and N ordinarily performsno useful function but will perform an emergency function that will beexplained in due course. LO20 completes a circuit for relay E which maybe traced from ground on the No. 1 contacts of relay El, No. 2 contactsof relay LO20, conductor 8, serially through the No. 1 back contacts ofthe individual link relays LK3, LKZ and LKI in the Y allotter, conductor9, winding of relay E to battery. Upon operating, relay E locks toground on the No. 1 contacts of relay LO20 and, at the same time, closesa circuit Vfor relays EI and E2 extending from ground on its contactstraced thereto from No. 1 contacts of relay LO20, No` 2 normally madecontacts of VArelay MS, the Windings of relays El and E2 in parallel tobattery. Relays EI and E2 operate but relay LO20, which operated fromground on the No. 1 contacts of relay El, now holds locked to batterythrough relay ST of the selected link, as previously traced, toconductor 6, winding of relay LO20 and its At the same time, relay- No.1 contacts, conductor 8 as traced to conduc-,f

tor 9, contacts of relay E to ground on the No. 1 contacts of relayLO20. Hence with the operation and locking of relay LO20 individual tocontrol station B, and with the operation of relays EI and E2, all otherlines may not receive service if calls are initiated thereat during thetime when station B is having a link assigned to it since, with relaysEI and E2 operated, no ground is available for completing the circuit ofthe relays L0- of the respective calling lines.

When relay EI operates, it completes a circuit for relay MS, saidcircuit being traced from ground on conductor I0, No. 14 contacts ofrelay EI, winding of relay MS to battery. Since relay MS hasslow-operating characteristics, it operates after an interval, opensthereby Fthe locking path of relay N, supplies holding ground over itsNo. 2 contactsior relays EI and E2 and, over its No. 3 contacts, appliesground on conductor I0 to conductor II. Ground on conductor II is usedto complete the circuit or the link select magnet 9 in virtue ofoperations which will be shortly described and which have been takingplace in the link as a result of the operation of relay ST therein.

In the event that, due to some trouble condition, relay E of the linkallotter fails to operate, relay MS cannot operate and ground will notbe applied to conductorv II over its No. 3 contacts. Under thesecir-cumstances it is desirable, if possible,rto complete the connectionand so emergency means are provided for applying ground to conductor I Iwhen relay MS fails to operate. It will be remembered that upon theoperation of relay LO20 a circuit was completed for relay N, and thatprior to the operation of relay MS, relay N caused the operation ofrelay M. Now when relay M operates, it opens the circuit of relay N, butrelay M remains naked over its No. 2 contacts to ground on conductor I0,and it will be observed that, with relay N normal and relay M operated,ground on conductor I0 is applied to conductor VII via the No. 1 frontcontacts of relay M and the No. 1 contacts of remy N.

Returning, now, to the operation of relay ST of allotted link No. 1, acircuit is completed for select magnet 9, the path of which may betraced from battery through the winding of said magnet, conductor I1,No. 2 contacts of relay B, No. 4 contacts ofY relay ST, conductor Il, tothe afore- `traced ground thereon. Select magnet 9 operates andconditions the group of cross-points on the ninth horizontal level .forselection, including cross-point 9 on vertical 20 through which thecalling loop will be extended into the link as shown hereinafter. Selectmagnet 9, upon operating, completes a contacts and common conductorI8.to the common windings of`relays S and SI causing said relays tooperate and complete a circuit for cutoilE relay C020, the circuit ofsaid relay being traced from ground on the No. 3 contacts of relays Sand SI, No. 3 contacts of relay L029, conductor I 9, winding of relayC020 to battery. Relay C020 upon operating closes an obvious circuit forhold magnet H020 of the vertical 20 .tol which line 20 (station B) isconnected and, because select magnet 9 is operated, operates cross-point9 on Vertical 20. This cross-point 9 remains op No. 2 contacts of saidrelay, No. 1 contacts of recircuit from ground over its lay T2,conductor SL'No. 3 "contactsV of crosspoint 9 on vertical 20 to ground.

Furthermore, although the release of relay L020 opened the originaloperating circuit of cutoi relay C020, said relay now remains lockedunder the control of the No. 3 contacts of the station telephoneinstrument and the contacts of key L, said locking circuit being tracedfrom ground on the No. 2 contacts of relayCOZIJ, No. 3 switchhookcontacts, serially through the normal contacts of the tr-unk keys TKI toTK4, contacts of key L, No. 4 contacts of cross-point 9 on vertical 20,winding of relay C020 to battery. Thus relay C020 is maintained in anoperated position, in turn holding operated magnet H020l which keepscross-point 9 closed.

Since cross-point 9 is operated, the line tip and ring conductors T andR are joined to the link tip and ring conductors LT and LR,respectively, over the No. 6 and No. 5 contactsof the operatedcross-point 9, respectively, and this joining of conductors completes anoperating path for relay A of the link which may be traced from batterythrough the lowerwinding of said relay, No. 2 back contacts of relay HS,conductor LT, No. 6 contacts of cross-point 9, line conductor T, overthe calling line loop, line conductor R, No. 15 contacts of cross-point9, conductorLR ofthe link, No. 3 back contacts of relay HS, upperwinding of relay A to ground. Relay AV operates andY completes a circuitfor relay .B which extends from ground on conductor SI, front contactsof relay A, No. 4 normally made continuity contacts of relay B, windingof relay B to` battery. Relay B operates and locks over its No. 4 frontcontacts to ground on conductor SI. Relay B, at its No. 2 contacts,opens conductor I'I thereby causing the release of the select magnet 9.However, since the hold magnet H023 is operated, cross-point 9 onvertical 23 remains closed. Relay B further completes a circuit fromground over its No. 8 contacts to a relay (not shown) in the powercharge circuit IIJII by means of which, when the relay is operated,circuits are closed thereby that will increase the charging rate to thelink power supply during the time that the link is being used and, overits No. and No. 6 contacts, connects ground to holding conductors 20 and2I for holding and operating certain other relays as noted below. Overits No. 1 contacts, relay B opens the locking circuit of relay yCHI inthe allotter circuit which, upon releasing, advances the common startconductor I over the No. 3 contacts of relay CH2, No. 2 contacts ofrelay CHI, No. 1 contacts of relay CH2 to conductor 'I' which furtherextends to relay ST of link No. 2.

It is now evident that if, at the time the call was initiated at stationB, `link No. 1 is busy or otherwise unavailable, relay CHI individual tothe link in the link allotter circuit would have been normal, and thestart wire I with ground applied thereto would have been joined toconductor 'I' of link No. 2 to cause the operation therein of relay STinthe same manner as that of relay ST in link No. 1 as alreadydescribed. 0n the other hand, if both links No. 1 and No. 2 are busy orotherwise unavailable, relay CH2, as well as relay CHI, would be normalsince their respective locking circuits would be opened at the No. 1contacts of relay B of their respective links. However, as soon asrelays CHI and CH2 are both normal, a circuit is completed for relay CH3which extends from battery through its winding, contacts of key KY3,conductor 2", No. 1 con- -tacts of relay B of link No.3, conductor' 3',to

ground over the No. 1 normally made contacts of relay CHI. lRelay CH3operates and, with relays CHI and CH2 normal, indicates that links No. 1and No. 2 are unavailable but that link No. 3 is. If a call is nowinitiated at a line station as, for example, station B, ground on startconductor I is extended to conductor 'I" which is connected to thewinding of relay ST of link No. 3, the path being from ground onconductor I, No. 4 contacts of relay CH2, No. 2` contacts of relay CH3,conductor 1", to the winding of relay ST of said link causing itsoperation and the connection of link No. 3 tothe calling line.

If all three links are unavailable,.relay CH3 will be normal as well asrelays CHI andVCHZ. Under these circumstances, the initiation of a callwill cause ground on the start conductor I to be applied to conductor 22via the No. 4 contacts of relay CH2, No. 1 contacts of relay CH3, No. 2contacts of relay CHI, No. 2 contacts of relay CH2, 4to conductor 22.This conductor extends (through bracket line I3) to the power, tone andalarm circuit III) and closes a circuit therein which causes a distinctlink busy tone to be applied to the conductors 23 and 24 extending tothe primary winding of the link busy tone transformer LBT. Since thesecondary winding of this transformer is connected to ground and iscompleted into a circuit over the line loop to battery through the uppernormally made contacts of the hold magnet HO- and through the winding ofthe line relay the subscriber at the calling station will hear the toneas an indication that, due to unavailable links, the connection cannotbe established. I

As soon as a link becomes available, say link No. l, then a circuit iscompleted for relay CHI which extends from battery through its winding,thence as traced to conductor 3, No. 5 contacts of relay CH2 to ground;Relay CI-II operates and locks to ground over its No. '3 contacts toreestablish the path of start conductor I to the winding of relay ST inreadiness for seizure on the next call. If link No. 2 becomes available,relay CH2 operates over a circuit traceable from battery through itswinding, thence as traced to conductor 3 to ground on the No. 3 normallymade contacts of relay CH3.

Returning, now, to the operation of relay ST of link No. 1 assumed tohave been taken into use, ground on the No. 3 contacts of said relaycompletes a circuit for relay LS! of its private link connector and thiscircuit is traced from ground on said contacts, conductor 58, winding ofrelay LSI, serially through the No. 2 normally made continuity contactsof relays LS2 and LS3 (the former being individual to link No. 2 and thelatter to link No. 3) to battery. Relay LSI operates, connects operatingbattery to its winding through its own No. 2 front contacts and, overits No. 1 front contacts, completes an obvious circuit for cut-in relayLCI which operates in consequence thereof.

The object in operating relays LSI and LCI at this time is to connectthe common alternating current pulse receiver and translator shown inFigs. 10 and 9, respectively, to the link taken into use and, when theformer circuit is so connected to the latter, the signal for theconsummation of the connection being the operation of relay LSI, saidreceiver must be made unavailable to other links. This is done byremoving the operating ground for relays LCZ and LC3 at the No. 1 backcontacts of relay LSI so that if either relay LS2 or LS3 should have itsoperating circuit established by relay ST of its correlated link, thecircuit of relay LC2 or LC3 will be cut off at the'No. 1 back contacts.of relay LSI.` On the other hand, if the rst calling link happens to beeither link No. 2 or link No. 3, then the corresponding operation ofeither relay LS2 or LS3 will cut oi the operating circuit of relay LSIat its respective No. 2 normally made continuity contacts. Under theseconditions, if link No. 1 is seized in the meanwhile, the failure ofrelay LSI to operate .will prevent the operation of relay LCI andthereby prevent the simultaneous .connection of the common alternatingcurrent receiver and translator to two calling links.

The alternatingcurrent,receiver of Fig. is adapted to receivealternating current impulses from a calling stationV equipped with analternating current generating device such as, for example, the deviceLG at station A (line 39).- Since the P. B..X exchange will contain telephone stations equipped with either a, device LG, as at station A, forproducing alternating frequency pulses designating the wanted line, orwith the usual dial LD, as at station B, for producing a series ofdirect current pulses indicative of the Wanted line, the link must beequipped to serve both types of stations although at the time it isconnectedto a, calling line the seized link has no way of telling whichtype of station is making the call. Hence the link must be prepared,initially, to receive either direct current pulses from aV dial LD oralternating current pulses from a generating device LG. Since the linkitself is normally arranged with a register to receive direct currentpulses, as will be shown shortly, the alternating current receivercommon to all links must be connected to a .calling linkV before thecalling subscriber can be advised, by an appropriate Warning tone, totransmit the called line designation. Accordingly, when relay LCIoperates, a circuit is completed for relay GR in the translator whichextends from ground 'on conductor ZI, No. l1 back contacts ofrelay C,conductor '15, No. Ll. contacts of relay LCI, cnductor l, winding wofrelay GR to battery. Relay GR operates and disconnects ground fromconductors 'H and '.FQ'WhiCh, as will be shown, areV connected to thecallingloop by the operation of relay ON. lA circuit is also completedfor relay ON .which may be traced from ground on the No. 5 contacts ofrelay LCI, conductorll, winding of relay ON to battery. RelayONYoperates and, over its No. `1 contacts, closes through a circuit fora low frequency tone derived from thetone oscillator 'I0 throughadjustable resistance pad 62 and transformer 6I. The path of` thiscircuit is traced as follows: From the lower terminal of the secondarywinding oi transformer 3|, conductor I4, No. 1 contacts of relay ST,conductor I5, No. 6 contacts of relay LCI, conductor IB, No. 3 contactsof relay RR, No. 2 contacts of relay RA, No. 1 contacts oi relay ON,conductor I2, through' the low-pass filter 33 to the upper Aterminal ofthe secondary winding of transformer 6I. The tone frequencies producedby Vthe oscillator 'I0 are thus induced over the secondarycircuit abovetraced.

Through a transformer arrangement (not shown) in the low-pass filter 63,the low frequencies are induced inthe closed circuit comprising thetransformer`68,`a transformer in said low-pass lter and, a transformerin high-passY filterSfI. Beyond thelsecon'dary winding of thetransformer 'in the`lter 64 'ar S able filter networks which aredesigned to pass only frequencies within the signal frequency band ofthe Vfrequencies that are produced by 'the station generator LG when thesame is operated. Hence the tone frequencies produced by oscillator "I0will notV pass into the volume limiter Q35 or into the enabler 80. Theywill, however, be induced into the secondary winding of transformervElisir said secondary winding is closed into an electrical system,which it isbecause conductors lI and 'I2 are but extensions of the lineconductors Tand R into the link and the alternating current receiverconnected thereto. The path is traced as follows: From the left side ofthe secondary winding of transformer 68, conductor ll, No. 2 contacts ofrelay ON, conductor l, No. 7 front contacts of relay LCI, conductor 5ft,condenser C2, No. 2 back contactsoi relay HS, conductor LT, No. 6contacts of cross-point 9 on vertical 20, conductor T, over` the loop ofstation B, con- .ductor R, No. 5 contacts of cross-point 9 on vertical2), conductor LR, No. 3 back contacts of relay HS, condenser C3,conductor 55, No. 8 front contacts of relay LCI, conductor lil, No. 5contacts of relay ON, conductor 'I2 to the right terminal of thesecondary winding of transformer G8. Inasmuch as the receiver of thetelephone instrument of station B is included in the above closedcircuit, vthe tone-induced thereover is heard by the attendant atstation B, which he understands as a signal to proceed with dialing thewanted number.

The control station attendant, upon receiving a tone, operates the dialLD to transmit the called line designation. In the present embodiment ofthe invention, it is assumed, as said before, that the capacity of theoffice isy twenty lines and that the numerical designation of each ofsaid lines extends from 20 to 39, inclusive, it being further assumedthat the control `'station B has a numerical vdesignationof 2,3 and thatstation Ahas a numerical designation of 39, the intermediate stations,equipped either with the dial LD or the device LG, bearing the numbersYY 2| to 38, inclusive. The calling subscriber there- Y fore dials awanted designation by dialing two digits, the rst of which may be a 2.or a 3 and the second of which may be any digit from 0 to 9.

Since it has been assumed that control station B is to be connected tothe called line A, the attendant at station B will rst'operate his dialto transmit three pulses forthe tens digit and thereafter nine pulsesfor the units. digit.

Asis well known, the operation of the dialLD makes and Ibreaks the,calling line .loop as many times as required .to produce the impulsescalled for. by the digits. Hence, upon dialing the digit 3, threeimpulses are produced andv the same will cause three successive releasesof relay A. When relay A releases on the first pulse it completes acircuit for relay PI which extends from `ground on conductor SI, theback contactsv of relay A, No. 3 contacts of relay B, No. 2 contacts ofrelay E, biackcontactslof relay P2, No. 2 back contacts of relay P3,winding of. relayjPIjto bata tery. Through the No. l back contacts ofrelay P3, the circuit further extends'to the Winding of slow-releaserelay C. Both Yrelays PI and C oper-- ate and short-circuit the lowerwinding of relay P2, ground to one side of this winding beingsuppliedover the No. 2 contacts of. relaysC .and

ground on the other side being supplied overthe No. 1Y contacts of relayPI to the Ybackcontacts Y of relay A. With the operation ofj'r'e'lay'PI,a

e Connected suitcirfcuitis completed for relay SW .which extends frombattery through its upper winding and the No, 2 normally made contacts,No. 5 back contacts of relay T2, No. 2 front contacts of relay PI,conductor 23, No. contacts of relay RT, conductor 24, No. 1 frontcontacts of relay C to lground on conductor 2 I. Relay SW operates andlocks over its upper winding and No. 2 front contacts to ground on theNo. 1 front contacts of relay/C. When relay A operates at thetermination of the rst pulse, the short-circuit around the lower windingof relay P2 is removed and this -relay operates in series with relay PIover a circuit path which may be traced from ground on the No. 2contacts of relay C, lower winding of relay P2, No. 1 contacts of relayPI, No. 2 contacts of relay P3, winding of relay PI to battery. Hence,after the rst pulse is terminated, relays PI, P2 and SW are operated,the latter being locked," as said before, to ground on conductor 2Ithrough the No. 1 front contacts of relay C which, being slow releasing,,remains in an operated condition between pulses.

On the beginning of the second pulse, relay A releases again andcompletes' a circuit path for Vrelay P3 which extends from ground on theback contacts of relay A, No. 3 contacts of relay B, No. 2 contacts ofrelay E, front contacts and upper winding of relay P2, winding of relayP3 to battery. vRelay P3' operates and releases relay'PI subsequent towhich a circuit is completed for relay T2 which extends from batterythrough the upper winding of said relay and its No. 3 normally madecontacts, No. 4 front contacts of relay SW, No. 2 back contacts of relayPI, conductor `23, and thence, as previously traced, to ground on theNo. 1 front contacts of relay C. Relay T2 operates, locks over both ofits windings in series through its No. 3 front contacts, conductor 28,No.5 contacts of relay HS, conductor 20 to ground on the No. 5 contactsof relay B and opens the locking circuitv of relay ST which releases.The release of relay ST at this time, however, results in no otherfunction.

At the termination of the second pulse, relay A reoperates and relays P2and P3 release so that,

l at the termination of the second pulse, relays PI,

P2 and P3 are normal, relay C is in an operated position due to itsslow-releasing characteristics, while relays SW and T2 are' locked. l

At the beginning of the thirdpulse, the release of relay A again causesthe operation of relay PI vand relay P2 is again short-*circuited but,in this case, a circuit is also completed for relay T3 which extendsfrom battery through its upper Winding and No. 2 normally madecontinuity contacts, No. 1 contacts of relay DC, No. 5 front contacts ofrelay SW, No. 5 front contacts o f relay T2, No. 2 `front contacts ofrelay PI, conductor 23, and thence, as already traced, to ground onthe'No. 1 front contacts of relay C. Relay T3 operates and, through itsNo. 2 front contacts, locks serially over both windings tov previouslytraced ground on conductor 28 from 'the No. 5 contacts of relay B. Atthe end ofthe pulse, relay A reoperates and relay P2 operates in serieswith relay PI, as previously described. However, since this is the thirdand last pulse ofthe tens digit, there will be a relatively longinterval before the transmission of the first pulse of the units digit,an interval which is sufcient to cause the release of relay C, followedby the release of relay SWand the release of relays PI and P2 which holdto ground over the No. 2 contacts of relay C. Y

'1t win be observed that the dialing cf the-numeral 3 as the tens digitof the called number has resulted in the operation and locking of relaysT2 and T3. If they tens digit had been a 2 instead of-a 3, the resultwould have been the operation and locking of relay T2 only. No provisionhas been made in the link for registering any tensdigit other than a 2or a 3` since the capacity of the exchange is assumed to be limited totwenty lines each having a numerical designation from 20 to 39. However,it is evident that if other numerical designations were to be used, orif the capacity of the exchange were to be increased to include morethanvtwenty lines,A the link circuit could easily be changed by any oneskilled in the art to cause the registration therein of any or all othervalues of the tens digit.

Prior to the dialing of the second or units digit, relay A is operatedVand relays PI, P2 and P3 are normal. Upon theiirst interruption of theline loop for the series of pulses of the second or units digit, relay Awill release followed by the operation of relays PI and C as previouslydescribed, while a circuit is now completed for relay CI-which extendsfrom battery through resistance RS, the Winding of said relay, No. 4normally made continuity contacts thereof, conductor 25, No. 10 backVcontacts of relay RT, conductor 26, No. 4 contacts of relay T2, No. 1contacts of relay SW, conductor 24, to ground on the No. 1 frontcontacts of relay C. Relay Cl Voperates in this circuit and locks overits No 4 front contacts, No. 5 contacts of relay HS to ground onconductor 20; AV circuit is now Y completed for relay CX, which extendsfrom battery, resistance CR, the winding of said relay and 'its No. 3normally made continuity contacts, No. 5 front contacts of relay CI, toground on the No. 5 contacts of relay B. Relay CX operates, locks tooperating ground over its No. 3 front contacts and, at its No. 1contacts, opens Y the circuit of relay LSI which releases to releaselbaclrcontacts of relay SW, No. 5front contacts 'of-relay T2; No.2 frontcontacts of relayPI and thence as traced to ground on the No. 1 frontcontacts of relay C; Relay I operates and locks with both of itswindings in series through its No. 5 front contacts, serially throughthe No. 4 continuity contacts of relay II, No. 5 continuity contacts Aofrelay III, No. 4 continuity contacts Vof relay IV, No. 5Ycontinuitycontacts of relay V, conductor 28, No.r 5 contacts of relayHS to ground on conductor 20,y Upon the termination of the pulse, relayAreoperates and relay P2 is operated serially with relayiPI.

On the secondpulse, relay Areleases, relay P3Aoperates in series withrelay P2 in consequence thereof, while relay PI releases as previouslydescribed., A circuit is vnow completed for relay II extending fromvbattery through its upper winding, No. 4 contacts of relayI, conductor29, No. fijlback contacts o f relay SWT-,Nd 2 back t contacts ofrrelayPIto, ground, as Y previously vtraced'tothe No. 2' front contacts of relayC.

a previously traced ground through the continuity contacts of relaysIII, IV and V. On the break of its own No. 4 continuity contacts, relayII releases relay I which thereby restores to normal. At the terminationof the second pulse,

relay A reoperates and relays P2 and P3 releaseI as previouslydescribed.

At the beginning of the third pulse, relay PI reoperates and a circuitis completed for relay lII which extends from battery through its upperwinding, No. 3 front contacts of relay II, No. 4 contacts of relay V,No. 3 contacts of relay IV, conductor 21, No. 5 back contacts of relaySW, No. 5 front contacts of relay T2, No. 2 front contacts of relay P I,conductor 23 to ground as previously traced. Relay III operates on itsupper winding, locks serially with its lower winding and No. 5 frontcontacts to a previously traced ground through the No. 4 and No. 5continuity contacts of relays IV and V, respectively, while, upon thebreak of its own No. 5 continuity contacts, it releases relay II whichthereby restores to normal.

On the fourth pulse, relay PI will be in a nonoperated position and,therefore, a circuit will be closed for relay IV which extends frombattery through its upper winding, No. 4 contacts of relay HI, conductor29, No. 4 back contacts of relay SW, No. 2 back contacts of relay PI toground as previously. traced. Relay IV operates on its upper winding andthen locks in series with its lower winding and No. 4 front contacts,through the No. 5 continuity contacts of relay V, to ground aspreviously traced. Upon the break of its No. 4 continuity contacts,relay IlI releases and restores to normal.

On the fth pulse, relay PI will loe Operated and a circuit will beclosed for/relay V which extends from battery through its upper Winding,No. 3 front contacts of relay IV, conductor 21, No. 5 back contacts ofrelay SW, No. 5 front contacts of relay T2, No. 2 front contacts ofrelay Pl to ground. Relay V operates on its upper winding and locks inseries with its lower winding through the No. 3 contacts of relay I, itsown No. 5 front contacts to ground as previously traced on the No. 1front contacts of relay C. When it breaks its own No. 5 continuitycontacts it releases relay IV which thereby restores to normal.

On the sixth pulse, relay PI will be in a nonoperated position whereupona circuit will be completed for relay VI which extends from batterythrough its upper Winding and No. 5 continuity contacts, No. 1 contactsof relay V, conductor 2S, No. 4 back contacts of relay SW, No. 2 backcontacts of relay Pl to ground. Relay.VI `operates on its upper windingand locks serially through its lower winding and No. 5 front contacts toground as previously traced on conductor 28. Relay V, however, willremain locked since its own locking circuit is independent of theoperated condition of relay VI.

On the seventh pulse, relay Pl will be in an operated position whereuponthe previously traced circuit for relay I will be established and relayI will operate in said circuit, locking thereafter in series with itslower winding and No. 5 contacts and through the previously identifiedcontacts of relays II, III and IV,Y and the No. 1 contacts of relay VIto ground on conductor 28. Relay V is released upon the operation ofrelay I.

On the eighth pulse, relay PI will be unoperated and a previously tracedcircuit for relay l1 will be established, which relay, upon operating,

eration of relay II, the locking circuit of relay I is opened at the No.4 continuity contacts of relay II and relay I thereby restores tonormal.

Relay VI remains locked toV ground on conductor 28.

On the ninth pulse, relay Pl will be operated and a previously tracedcircuit for relay III is established causing said relay to operate onits upper winding and then lock in series with its lower winding and No.5 contacts, No. 4 continuity contacts of relay IV, No. 5 contacts ofrelayV to ground on conductor 28. Upon the operation of relay III, relayII restores. locked to ground on conductor 28.

On the last or zero pulse, relay Pl will be normal and a previouslytraced circuitI will be established for relay IV which operatesthereover on its upper winding and then locks serially through its lowerwinding and No. 4 continuity contacts, No. 5 continuity contacts ofrelay V, to ground on conductor 28.

On the last or zero pulse, relay Pl will be nor? may and a previouslytraced circuit will be established for relay IV which operates thereoveron its upper winding and then locks serially through its lower windingand No. 4 continuity contacts, No. 5 continuity contacts of relay V, toground on conductor 28. Relay VI is still locked to ground on conductor28.

Thus the pulses of the second or units digitare registered in the relaysI-VI .of Fig'. '1, the relay, or relays, operated depending upon thenumber of pulses received. The relationship between the number of pulsesand the relays operated to correspond thereto is shown in the followingtable:

Relay op- I tt.

It has been assumed that the called subscribers number is 39 andtherefore in respect to the units digit, relays III and VI will havebeen operated.

At the end of the last pulse of the second digit with relay Areoperated, relay C will release and a circuit is then closed for relayDC which eX- tends from battery through its lower winding and No. 5continuity contacts, conductor 39, No.2 contacts of relay Cl, conductor15, No. 1 back contacts of relay C to ground on conductor 2l. RelayDCoperates on its lower winding and locks through its No. 5 front contactsin series with its upper Winding to ground as previously traced onconductor 28. Relay DC, upon operating, completes a path for relay SWextending from bat-V tery through its upper and lower windings inseries, No. 2 front contacts of relay DC to ground on conductor 28.Relay DC also connects batterythrough the lower winding of relay BY to aconductor which, depending upon the numerical register relays in Fig. '1which have been operated in response to the units digit, extends to anarmature of the hold magnet of the vertical associated with the calledline which, in this case,

Relay VI remains will be hold magnet HO39. This path istraced asfollows: Battery through the lower winding of relay BY, No. 4 continuitycontacts of said relay, No. 1 front contacts of relay CI, No, 4 contactsof relay DC, No. 1 front contacts of relay T3,v

conductor 3D, No. 4 front contacts of relay VI, conductor 3|, No. 6contacts of relay DC, conductor 32, No. 6 contacts of relayllL'conductor 33, lower armature and contact of hold magnet H039 to thewinding of relay C039. The object of this circuit is to test for theidle or busy condition of the called line. Should this line be busy,hold magnet H039 will be operated, whereupon it will apply ground toconductor 33 through its lower front contacts and causethereby theoperation of relay BY which then locks through its No. 4 front contactsserially through its upper winding, No, 5 contacts of relay HS to groundon conductor 29. Relay BY applies ground through its No. 1 contacts toconductor 34 extending to the power, tone and alarm circuit |I wherebycircuits are closed therein to apply a busy tone source tovconductor 35.This conductor extends over the No. 2 contacts of relay BY to one sideof condenser C2 through which the tone current passes over the No. 2back contacts of relay HS, conductor LT, over the loop previously tracedto conductor LR, No. 3 back contacts of relay HS, upper winding of relayA to ground. The busy tone thus furnished the calling station 20indicates to the attendant thereat that the called line is busy,whereupon he Yrestores the telephone instrument upon the cradle andthereby opens the circuit of relay A, the release of which initiates therestoration of the apparatus as dey scribed hereinafter.

Assuming, ho-wever, that the` called lineis not busy, then hold magnetH039 willA loe normal and relay BY will not be caused to operate. Inthis case a circuit is closed for relay LKI of the link in the callallotter, whichY circuit extends from battery through the winding ofsaid relay, conductor 33, No. 3 contacts of relay BY, No. 3 contacts ofrelay SW, No. 3 contacts of relay CI, conductor 3l to ground on the No.11 contactsof relay EI. Relay LKI operates, completes a cir-V cuit forrelay BI in the call allotter, Ywhich circuit extends from batterythrough the winding of relay Bi, conductor 38, No. contactsofrelay LKI,conductor 39, No. 2 contacts ofY relay CI, conductor '15, No. l backcontacts of relay C to ground on conductor 2l, and: opens the seriallocking path oi. all relays LO- which, should any of them operate inresponse to the initiation of a call during the time that a link issetting up the terminating end of a connection,V will be prevented fromlocking at the time relays EI and E2 operate in the manner previouslydescribed; The failure of a relay LO- to lock will then prevent groundfrom being` applied to conductor lI over the contacts of relay MS. Inthis manner, a line which calls during the setting up of a connectionwill be preventedfrom. interfering and, of course, willA also be deniedservice until the previous connection has been set up; Relay LKI alsocompletes a circuit for relay EA of the call allotter which traces frombattery through its winding, conductor 9, No. 1 front contacts ofrelayLKi, conductor 3l, to ground on the No. 1l contacts of relay El.Relay lil'` now operates relays El, E2 and MS as previously describedAand, when relay MS operatesa circuit iscompleted` for select magnet 3which extends from battery through theV winding of said magnet, backycontacts of relay TKLI, conductor 49NQQ6 contacts of relay LKI conductor4|, No. 1 contacts of relay BI, conductor Il, No. 3 contacts of relayMS, conductor I9, toV ground on the No. 3 contacts of relay LKI. Selectmagnet 8 operates, conditions the horizontal cross-points on the eighthlevel for selection. and completes a circuit from ground through thecontacts of said magnet, conductor la, windings of relays S and SI inparallel, to battery, causing said relays to operate. The operation ofrelay S connects ground through its No. 2 contacts, conductor 42, theNo. 4 contacts of relay LKI, conductor 43 to the common terminal ofresistance RS and the winding of relay CI causing the release of thelatter. Upon the release of relay CI, ground is applied to conductor 33which, as previously traced, is connected to the Winding of relay C039of the called line A. Relay C039 operates and completes an obviouscircuit for. hold magnet H039 which operates toY close cross-point 8 onVertical 39. The operation of the hold magnet H039 disconnects operatingground for relay-C039, but this relay now holds over the No. 4 contactsof cross-point 8 of vertical 3.9, conductor S, No. 3 `back contacts ofrelayV E, No. 7 contacts of relay B, front contacts of relay A (which islbeing held over the calling line loop from station B) to ground onconductor Si as previously traced thereto. Operated cross-points 8 and 9on verticals 39 and 2D, respectively, eiect therconnection between thecalling contro-l station B and the called station A.

Ground on conductor S2 applied thereto by the closure of the No. 3contacts of cross-point 8 on vertical 39 completes a circuit for relaySP, the path of which may be traced from ground on said conductor, No. 2front contacts of relay T2, No. contacts of relay BY, winding of relaySP to orattery. Relay SP operates and connects ringing current applied'to conductor 41 within the bracket line I3 from the power and ringingcircuit IID, through the No. 3 contacts of relay RTR and lower windingthereof, No. 3 front contacts of relay SP., conductor 48, No. 5 contactof crossfpoint 8 of vertical 39, ring conductor RI of; the calledstation A, over the loop of said station, tip conductor TI, No. 6contacts of said cross-point 8, conductor 49No. 2 front contacts vofVVrelay SP, conductor 5i] within the bracket line I3 to ground appliedthereto in the power and ringing circuit IIIl. Ringing current is thusapplied to the called subscribers line and an audible ringing tone isprovided for the calling station, the circuit of saidtone extending fromone side. of -ringing tone circuit (not shown) in the power and` ringingcircuit III), conductor III within bracket line I3, No. 5- contacts ofrelay SP, condenser C6, condenser C2, and-thence as traced over thecalling loop to ground through the upper winding of relay A. 'Thecontrol operator at station B thus hears the ringing tone. When the callis answered, relay RTR operates and locks over its upper winding and No.2 contacts to ground on the No. 4 front contacts of relay SP, andfurtherv completes a circuit for relay HS which extends from batterythrough its winding,

conductor 5I, contacts VI and 2 in cross-point 8 e of vertical- 39,Vconductor 52,l No. 1 contacts of relay RTR to ground on conductor 2 I.Relay HS operates and, by-opening its No. 5 contacts, disconnects theground `Which holdsrelays SW, T2, T3, DC and the register relays III andVI operated. The release of relay T2 releases relay SP which, in turn,releases relay R'IR'andl connects the supervisory relay E to the calledline.` The circuit of relay E is follows: Batteryfthrough

